During the past 10 years there has been considerable interest in isolating and characterizing the numerous species of cytochrome P-450. Separations are most often accomplished by a combination of several types of column chromatography. Progress in this field, however, has been greatly hampered by the methodology for assaying cytochrome P-450. For example, the following steps are involved in an assay of a column fraction for cytochrome P-450. 1) The sample is reduced with sodium dithionite; 2) the reduced sample is added to a sample and reference cuvette, and a background spectrum is run; 3) carbon monoxide is bubbled through the sample cuvette, and a different spectrum is recorded; 4) finally, the concentration of cytochrome P-450 is determined. We have designed a flow cell which in combination with a microprocesser unit may be used to assay cytochrome P-450 as it is eluted from columns. This innovation should increase the resolution and sensitivity of the various column chromatography procedures used in the characterization and purification of cytochrome P-450 and decrease the time required for analyses.